In the conventional radio communication system, a pilot signal is used as a known signal to estimate the channel. In the communication with a plurality of terminals sharing a radio resource, a method of multiplexing the pilot signal at predetermined intervals on the transmission data multiplexed for multiple users is known as a method of multiplexing the pilot signal shared and the transmission data to a plurality of terminals. An explanation is made below about the signal multiplexing method described in Technical Report TR25.892 of Standard Association 3GPP with reference to FIG. 1.
A resource assignment unit 802 determines the assignment of the radio resource to each terminal unit and outputs a resource assignment signal SRA. A multiplex signal generating unit 103 supplied with the resource assignment signal SRA multiplexes the pilot data and the transmission data and outputs a transmission signal STX.
FIG. 4 shows an example of the configuration of the multiplex signal generating unit 103 using OFDM (Orthogonal Frequency Division Multiplexing) as a radio transmission method. OFDM is one of the radio transmission methods having a superior multipath resistance characteristic, in which the entire band is divided into a plurality of subcarriers, and by inserting guard intervals and deleting the guard intervals at the receiving end, the inter-symbol interference due to the multipath is removed.
A pilot generating unit 201 generates and outputs a pilot signal SPI. Data generating units 202 to 204 output transmission data STXD1 to STXDN to terminals 1 to N. Symbol mapping units 205 to 207, supplied with the transmission data STXD1 to STXDN, map the data to the transmission symbols and output transmission symbol signals STXS1 to STXSN, respectively.
A pilot multiplexer 208, supplied with the pilot signal SPI as an input, outputs pilot multiplex signals SMP1 to SMPL. The data multiplexer 209, supplied with the transmission symbol signals STXS1 to STXSN and the resource assignment signal SRA, multiplexes the transmission symbol signals STXS1 to STXSN in accordance with the resource assignment signal SRA, and outputs data multiplex signals SMD1 to SMDL. The pilot multiplex signals SMP1 to SMPL and the data multiplex signals SMD1 to SMDL are added to each other thereby to generate inverse Fourier transform unit input signals SIFTI1 to SIFTIN.
The inverse Fourier transform unit 210, supplied with the inverse Fourier transform unit input signals SIFTI1 to SIFTIN, conducts the inverse Fourier transform and outputs an inverse Fourier transform unit output signal SIFTO. A guard interval insertion unit 211, supplied with an inverse Fourier transform unit output signal SIFTO, inserts a guard interval and outputs a transmission signal STX.
With the configuration described above, as shown in FIG. 2, for example, a transmission signal with pilot signals multiplexed at predetermined intervals on time axis and frequency axis is generated. At the receiving end, the channel is estimated using the pilot signal, and the portion of the channel with no pilot signal multiplexed is estimated by linear interpolation or the like based on two points of the estimated value on the channel portion where the pilot signal is inserted.
Also, a radio transmission method is available for adaptively selecting the direction of diffusion (time axis, frequency axis) of the radio resource at the transmitting end in accordance with the channel change (see, for example, Patent Document 1).
Patent Document 1: JP-A-2003-304220
Disclosure Of The Invention
At terminals high in moving speed or in a harsh environment with multipath interference, however, the channel frequently changes on both time axis and frequency axis. In the case where a radio resource distant from the pilot signal multiplex position on time axis or frequency axis are assigned to such terminals for data communication, therefore, the resource assignment method described above poses the problem that the channel estimation accuracy at the receiving end is deteriorated. Although this accuracy can be improved by reducing the intervals at which the pilot signals are inserted, the problem of deterioration of transmission efficiency arises.
In view of the above, an object of this invention is to provide a resource assignment method for a communication system adapted to the channel change which improves the channel estimation accuracy without reducing the data transmission efficiency.
In order to solve the aforementioned problem, the radio communication apparatus according to this invention includes a resource assignment unit supplied with a first to a Nth (N: arbitrary natural number) channel information corresponding to a first to a Nth terminal units for determining the resource assignment to the first to Nth terminal units and outputting a resource assignment signal, and a multiplex signal generating unit supplied with the resource assignment signal for multiplexing the pilot signal and the transmission data and outputting a transmission signal. The radio communication apparatus detects a change of channel of each terminal unit and assigns preferentially a resource nearby a multiplex position of a pilot signal to the terminal unit making a larger change of propagation.
With this configuration, estimation accuracy of the channel is improved without causing deterioration of the data transmission efficiency.
Effect Of The Invention
This invention, with the configuration and the operation described below, produces the effect of improving the channel estimation accuracy without reducing the data transmission efficiency.